The present invention pertains to the field of art involving video systems having a light control wheel for generating color or black and white video images, including video-equipped endoscope and borescope systems.
In typical video-equipped endoscope and borescope systems, a light source is required to illuminate a target in the object plane of the viewing optics. Generally, the white light generated from the light source is projected in the form of a beam and is optically coupled to a viewing probe which is configured to transmit the light into the target area. The incident light reflected from the target is received by a viewing head of the probe which causes an image to be focussed upon an imaging device within the probe. The imaging device receives the image and converts it into electrical signals to be processed. A more detailed description of such systems is provided in U.S. Pat. Nos. 4,532,918 to Wheeler and 4,539,586 to Danna et al.
These systems may employ a light control wheel such as a color filter wheel or a shutter or chopper wheel between the light source and the viewing probe. A color filter wheel can be arranged to rotate a series of different colored filters through the beam of white light emitted by the light source to produce incident source light in a sequence of separate colors to be transmitted to the target area. The reflected light from the target is received by the viewing head as color separated images of the target. Accordingly, a field sequential color video signal may be produced.
The color filter wheel is generally configured with color filters spaced apart from each other in a circular pattern. The regions between the filters generally do not permit transmission of light through the wheel. Hence, these regions act as shutters on a camera system, and are usually employed in that manner. That is, during the period of time the light beam is blocked by these regions, the imaging device, having received a color separated image, is read out by conventional video processing circuitry. A more detailed description of such systems is provided in U.S. Pat. Nos. 4,546,379 and 4,523,224.
In a black and white video system, the unfiltered white light from the light source is transmitted to the target area. However, the necessity for a shutter function remains. This function can be achieved by using a shutter or chopper wheel configured like a fan with flat blades spaced equidistant apart. The beam of light passes between the blades to illuminate the target and generate an image of the target. While the beam is blocked by a blade of the wheel, the received image is read from the imaging device.
In many endoscope and borescope applications calling for viewing a target within a range of twelve inches, color video image generation will produce the optimum picture for diagnostic purposes. On the other hand, when the application calls for viewing targets greater than eighteen inches, black and white image generation will produce the optimum picture. In many practical applications of these instruments, the target range can vary from zero to greater than three feet. Therefore, for optimum viewing of video images, both color and black and white systems are required. Conceivably, a color system can be converted into a black and white system by replacing the color filter wheel with a shutter wheel. However, this approach frequently requires the use of special tools and is not practical for non-technical or inexperienced operators of the systems.
Moreover, it may be desirable to utilize the white light source in the video-equipped endoscope or borescope system as an auxiliary light source for another video system or for a direct viewing scope, such as a borescope. However, for conventional video-equipped systems, this is not possible since the light coupled out of the system is either chopped or chopped and colored. Conceivably, in a black and white video system, the rotating shutter wheel could be paused so the beam of light is permitted to pass between adjacent shutter blades. However, this would require the use of additional control circuitry and a breaking or positioning mechanism, which adds to the complexity and cost of the system.